Designing eco-evolutionary experiments for restoration projects: Opportunities and constraints revealed during stickleback introductions.

Eco-evolutionary experiments are typically conducted in semi-unnatural controlled settings, such as mesocosms; yet inferences about how evolution and ecology interact in the real world would surely benefit from experiments in natural uncontrolled settings. Opportunities for such experiments are rare but do arise in the context of restoration ecology-where different "types" of a given species can be introduced into different "replicate" locations. Designing such experiments requires wrestling with consequential questions. (Q1) Which specific "types" of a focal species should be introduced to the restoration location? (Q2) How many sources of each type should be used-and should they be mixed together? (Q3) Which specific source populations should be used? (Q4) Which type(s) or population(s) should be introduced into which restoration sites? We recently grappled with these questions when designing an eco-evolutionary experiment with threespine stickleback (Gasterosteus aculeatus) introduced into nine small lakes and ponds on the Kenai Peninsula in Alaska that required restoration. After considering the options at length, we decided to use benthic versus limnetic ecotypes (Q1) to create a mixed group of colonists from four source populations of each ecotype (Q2), where ecotypes were identified based on trophic morphology (Q3), and were then introduced into nine restoration lakes scaled by lake size (Q4). We hope that outlining the alternatives and resulting choices will make the rationales clear for future studies leveraging our experiment, while also proving useful for investigators considering similar experiments in the future.

Divergence in Reproductive Behaviors Is Associated with the Evolutionary Loss of Parental Care.

AbstractThe mechanisms underlying the divergence of reproductive strategies between closely related species are still poorly understood. Additionally, it is unclear which selective factors drive the evolution of reproductive behavioral variation and how these traits coevolve, particularly during early divergence. To address these questions, we quantified behavioral differences in a recently diverged pair of Nova Scotian three-spined stickleback (Gasterosteus aculeatus) populations, which vary in parental care, with one population displaying paternal care and the other lacking this. We compared both populations, and a full reciprocal F1 hybrid cross, across four major reproductive stages: territoriality, nesting, courtship, and parenting. We identified significant divergence in a suite of heritable behaviors. Importantly, F1 hybrids exhibited a mix of behavioral patterns, some of which suggest sex linkage. This system offers fresh insights into the coevolutionary dynamics of reproductive behaviors during early divergence and offers support for the hypothesis that coevolutionary feedback between sexual selection and parental care can drive rapid evolution of reproductive strategies.

Predator-induced transgenerational plasticity of parental care behaviour in male three-spined stickleback fish across two generations.

Parental care is a critical determinant of offspring fitness, and parents adjust their care in response to ecological challenges, including predation risk. The experiences of both mothers and fathers can influence phenotypes of future generations (transgenerational plasticity). If it is adaptive for parents to alter parental care in response to predation risk, then we expect F1 and F2 offspring who receive transgenerational cues of predation risk to shift their parental care behaviour if these ancestral cues reliably predict a similarly risky environment as their F0 parents. Here, we used three-spined sticklebacks (Gasterosteus aculeatus) to understand how paternal exposure to predation risk prior to mating alters reproductive traits and parental care behaviour in unexposed F1 sons and F2 grandsons. Sons of predator-exposed fathers took more attempts to mate than sons of control fathers. F1 sons and F2 grandsons with two (maternal and paternal) predator-exposed grandfathers shifted their paternal care (fanning) behaviour in strikingly similar ways: they fanned less initially, but fanned more near egg hatching. This shift in fanning behaviour matches shifts observed in response to direct exposure to predation risk, suggesting a highly conserved response to pre-fertilization predator exposure that persists from the F0 to the F1 and F2 generations.

The evolution of decision-making mechanisms under competing demands.

Animals in nature are constantly managing multiple demands, and decisions about how to adjust behavior in response to ecologically relevant demands is critical for fitness. Evidence for behavioral correlations across functional contexts (behavioral syndromes) and growing appreciation for shared proximate substrates of behavior prompts novel questions about the existence of distinct neural, molecular, and genetic mechanisms involved in decision-making. Those proximate mechanisms are likely to be an important target of selection, but little is known about how they evolve, their evolutionary history, or where they harbor genetic variation. Herein I provide a conceptual framework for understanding the evolution of mechanisms for decision-making, highlighting insights on decision-making in humans and model organisms, and sketch an emerging synthesis.

Recovering from a broken heart.

A molecular signature found in the brains of monogamous prairie voles begins to decay after prolonged separation from their partner.

Insights into Parental Care from Studies on Non-mammalian Vertebrates.

Parental care has attracted attention from both proximate and ultimate perspectives. While understanding the adaptive significance of care has been the focus of work in diverse organisms in behavioral ecology, most of what we know about the proximate mechanisms underlying parental care behavior comes from studies in mammals. Although studies on mammals have greatly improved our understanding of care, viewing parental care solely through a mammalian lens can limit our understanding. Here, we draw upon examples from non-mammalian vertebrate systems to show that in many ways mammals are the exception rather than the rule for caregiving: across vertebrates, maternal care is often not the ancestral or the most common mode of care and fathering is not derivative of mothering. Embracing the diversity of parental care can improve our understanding of both the proximate basis and adaptive significance of parental care and the affective processes involved in caregiving.

Predator-induced transgenerational plasticity in animals: a meta-analysis.

There is growing evidence that the environment experienced by one generation can influence phenotypes in the next generation via transgenerational plasticity (TGP). One of the best-studied examples of TGP in animals is predator-induced transgenerational plasticity, whereby exposing parents to predation risk triggers changes in offspring phenotypes. Yet, there is a lack of general consensus synthesizing the predator-prey literature with existing theory pertaining to ecology and evolution of TGP. Here, we apply a meta-analysis to the sizable literature on predator-induced TGP (441 effect sizes from 29 species and 49 studies) to explore five hypotheses about the magnitude, form and direction of predator-induced TGP. Hypothesis #1: the strength of predator-induced TGP should vary with the number of predator cues. Hypothesis #2: the strength of predator-induced TGP should vary with reproductive mode. Hypothesis #3: the strength and direction of predator-induced TGP should vary among offspring phenotypic traits because some traits are more plastic than others. Hypothesis #4: the strength of predator-induced TGP should wane over ontogeny. Hypothesis #5: predator-induced TGP should generate adaptive phenotypes that should be more evident when offspring are themselves exposed to risk. We found strong evidence for predator-induced TGP overall, but no evidence that parental predator exposure causes offspring traits to change in a particular direction. Additionally, we found little evidence in support of any of the specific hypotheses. We infer that the failure to find consistent evidence reflects the heterogeneous nature of the phenomena, and the highly diverse experimental designs used to study it. Together, these findings set an agenda for future work in this area.

A Behavioral Syndrome Linking Boldness and Flexibility Facilitates Invasion Success in Sticklebacks.

AbstractFor a species to expand its range, it needs to be good at dispersing and also capable of exploiting resources and adapting to different environments. Therefore, behavioral and cognitive traits could play key roles in facilitating invasion success. Marine threespined sticklebacks (Gasterosteus aculeatus) have repeatedly colonized freshwater environments and rapidly adapted to them. Here, by comparing the behavior of hundreds of lab-reared sticklebacks from six different populations, we show that marine sticklebacks are bold, while sticklebacks that have become established in freshwater lakes are flexible. Moreover, boldness and flexibility are negatively correlated with one another at the individual, family, and population levels. These results support the hypothesis that boldness is favored in invaders during the initial dispersal stage, while flexibility is favored in recent immigrants during the establishment stage, and they suggest that the link between boldness and flexibility facilitates success during both the dispersal stage and the establishment stage. This study adds to the growing body of work showing the importance of behavioral correlations in facilitating colonization success in sticklebacks and other organisms.

Vertical transmission of horizontally acquired social information in sticklebacks: implications for transgenerational plasticity.

There is growing evidence that offspring receive information about their environment vertically, i.e. from their parents (environmental parental effects or transgenerational plasticity). For example, parents exposed to predation risk may produce offspring with heightened antipredator defences. At the same time, organisms can gain information about the environment horizontally, from conspecifics. In this study, we provide some of the first evidence that horizontally acquired social information can be transmitted vertically across generations. Three-spined stickleback (Gasterosteus aculeatus) fathers produced larval offspring with altered antipredator behaviour when fathers received visual and olfactory cues from predator-chased neighbours. Although fathers did not personally witness their neighbours being chased (i.e. they never saw the predator), changes in offspring traits were similar to those induced by direct paternal exposure to predation risk. These findings suggest that two different non-genetic pathways (horizontal transfer of social information, vertical transfer via sperm-mediated paternal effects) can combine to affect offspring phenotypes. The implications of simultaneous horizontal and vertical transmission are widely appreciated in the context of disease and culture; our results suggest that they could be equally important for the maintenance of phenotypic variation and could have profound consequences for the rate at which information flows within and across generations.

The interplay between sperm-mediated and care-mediated paternal effects in threespine sticklebacks.

The environment experienced by one generation can influence the phenotypes of future generations. Because parental cues can be conveyed to offspring at multiple points in time, ranging from fertilization to posthatching/parturition, offspring can potentially receive multiple cues from their parents via different mechanisms. We have relatively little information regarding how different mechanisms operate in isolation and in tandem, but it is possible, for example, that offspring phenotypes induced by nongenetic changes to gametes may be amplified by, mitigated by, or depend upon parental care. Here, we manipulated paternal experience with predation risk prior to fertilization in threespine stickleback, Gasterosteus aculeatus, and then examined the potential of paternal care to mitigate and/or amplify sperm-mediated paternal effects. Specifically, we compared (1) offspring of predator-exposed fathers who were reared without paternal care, (2) offspring of predator-exposed fathers who were reared with paternal care, (3) offspring of control (unexposed) fathers who were reared without paternal care and (4) offspring of control fathers who were reared with paternal care. We found that offspring of predator-exposed fathers were less active and had higher cortisol following a simulated predator attack. Although predator-exposed males shifted their paternal care behaviours - reduced fanning early in egg development and increased fanning right before egg hatching compared to control males - this shift in paternal behavior did not appear to affect offspring traits. This suggests that paternal care neither amplifies nor compensates for these phenotypic effects induced by sperm and that nongenetic changes induced by sperm may occur independently of nongenetic changes induced by paternal care. Overall, these results underscore the importance of considering how parents may have multiple nongenetic mechanisms by which they can influence offspring.

Back to the basics? Transcriptomics offers integrative insights into the role of space, time and the environment for gene expression and behaviour.

Fuelled by the ongoing genomic revolution, broadscale RNA expression surveys are fast replacing studies targeting one or a few genes to understand the molecular basis of behaviour. Yet, the timescale of RNA-sequencing experiments and the dynamics of neural gene activation are insufficient to drive real-time switches between behavioural states. Moreover, the spatial, functional and transcriptional complexity of the brain (the most commonly targeted tissue in studies of behaviour) further complicates inference. We argue that a Central Dogma-like 'back-to-basics' assumption that gene expression changes cause behaviour leaves some of the most important aspects of gene-behaviour relationships unexplored, including the roles of environmental influences, timing and feedback from behaviour-and the environmental shifts it causes-to neural gene expression. No perfect experimental solutions exist but we advocate that explicit consideration, exploration and discussion of these factors will pave the way toward a richer understanding of the complicated relationships between genes, environments, brain gene expression and behaviour over developmental and evolutionary timescales.

Combining information from parental and personal experiences: Simple processes generate diverse outcomes.

Experiences of parents and/or offspring are often assumed to affect the development of trait values in offspring because they provide information about the external environment. However, it is currently unclear how information from parental and offspring experiences might jointly affect the information-states that provide the foundation for the offspring phenotypes observed in empirical studies of developmental plasticity in response to environmental cues. We analyze Bayesian models designed to mimic fully-factorial experimental studies of trans and within- generational plasticity (TWP), in which parents, offspring, both or neither are exposed to cues from predators, to determine how different durations of cue exposure for parents and offspring, the devaluation of information from parents or the degradation of information from parents would affect offspring estimates of environmental states related to risk of predation at the end of such experiments. We show that the effects of different cue durations, the devaluation of information from parents, and the degradation of information from parents on offspring estimates are all expected to vary as a function of interactions with two other key components of information-based models of TWP: parental priors and the relative cue reliability in the different treatments. Our results suggest empiricists should expect to observe considerable variation in the patterns observed in experimental studies of TWP based on simple principles of information-updating, without needing to invoke additional assumptions about costs, tradeoffs, development constraints, the fitness consequences of different trait values, or other factors.

The specificity of sperm-mediated paternal effects in threespine sticklebacks.

Parental effects may help offspring respond to challenging environments, but whether parental exposure to different environmental challenges induces similar responses in offspring is largely unknown. We compared the offspring of threespine stickleback (Gasterosteus aculeatus) fathers who had been exposed to a potentially threatening stimulus (net), a native predator (sculpin), or who had been left unexposed (control). Relative to offspring of control fathers, offspring of sculpin-exposed fathers were more responsive (greater change in activity) to a simulated sculpin predator attack, while offspring of net-exposed fathers were less responsive (fewer antipredator behaviors) and showed altered stress responses compared to the control. To evaluate whether parental exposure primes offspring to respond to specific stimuli (e.g., offspring of net-exposed fathers respond most strongly to a net), we then exposed offspring of each paternal treatment to nets, native sculpin models, or non-native trout models. Paternal treatment did not influence offspring response to different stimuli; instead, offspring were generally more responsive to the native sculpin predator compared to nets or non-native trout predator, suggesting that sticklebacks have innate predator recognition of native predators. Collectively, these results underscore that, while parental exposure to non-ecologically relevant stressors elicits effects in intergenerational studies, these findings may not mirror those produced when parents encounter ecologically relevant stressors. Knowing that parental effects can be predator-specific furthers our understanding of the ways in which parental effects may evolve to be adaptive and suggests the potential for transgenerational plasticity to affect how animals respond to human induced environmental change, including non-native predators.

Sex-specific plasticity across generations II: Grandpaternal effects are lineage specific and sex specific.

Transgenerational plasticity (TGP) occurs when the environment encountered by one generation (F0) alters the phenotypes of one or more future generations (e.g. F1 and F2). Sex selective TGP, via specific lineages or to only male or female descendants, has been underexplored in natural systems, and may be adaptive if it allows past generations to fine-tune the phenotypes of future generations in response to sex-specific life-history strategies. We sought to understand if exposing males to predation risk can influence grandoffspring via sperm in three-spined stickleback Gasterosteus aculeatus. We specifically tested the hypothesis that grandparental effects are transmitted in a sex-specific way down the male lineage, from paternal grandfathers to F2 males. We reared F1 offspring of unexposed and predator-exposed F0 males under 'control' conditions and used them to generate F2s with control grandfathers, a predator-exposed maternal grandfather (i.e. predator-exposed F0 males to F1 daughters to F2s), a predator-exposed paternal grandfather (i.e. predator-exposed F0 males to F1 sons to F2s) or two predator-exposed grandfathers. We then assayed male and female F2s for a variety of traits related to antipredator defence. We found little evidence that transgenerational effects were mediated to only male descendants via the paternal lineage. Instead, grandpaternal effects depended on lineage and were mediated largely across sexes, from F1 males to F2 females and from F1 females to F2 males. When their paternal grandfather was exposed to predation risk, female F2s were heavier and showed a reduced change in behaviour in response to a simulated predator attack relative to grandoffspring of control, unexposed grandparents. In contrast, male F2s showed reduced antipredator behaviour when their maternal grandfather was exposed to predation risk. However, these patterns were only evident when one grandfather, but not both grandfathers, was exposed to predation risk, suggesting the potential for non-additive interactions across lineages. If sex-specific and lineage effects are common, then grandparental effects are likely underestimated in the literature. These results draw attention to the importance of sex-selective inheritance of environmental effects and raise new questions about the proximate and ultimate causes of selective transmission across generations.

Sex-specific plasticity across generations I: Maternal and paternal effects on sons and daughters.

Intergenerational plasticity or parental effects-when parental environments alter the phenotype of future generations-can influence how organisms cope with environmental change. An intriguing, underexplored possibility is that sex-of both the parent and the offspring-plays an important role in driving the evolution of intergenerational plasticity in both adaptive and non-adaptive ways. Here, we evaluate the potential for sex-specific parental effects in a freshwater population of three-spined sticklebacks Gasterosteus aculeatus by independently and jointly manipulating maternal and paternal experiences and separately evaluating their phenotypic effects in sons versus daughters. We tested the adaptive hypothesis that daughters are more responsive to cues from their mother, whereas sons are more responsive to cues from their father. We exposed mothers, fathers or both parents to visual cues of predation risk and measured offspring antipredator traits and brain gene expression. Predator-exposed fathers produced sons that were more risk-prone, whereas predator-exposed mothers produced more anxious sons and daughters. Furthermore, maternal and paternal effects on offspring survival were non-additive: offspring with a predator-exposed father, but not two predator-exposed parents, had lower survival against live predators. There were also strong sex-specific effects on brain gene expression: exposing mothers versus fathers to predation risk activated different transcriptional profiles in their offspring, and sons and daughters strongly differed in the ways in which their brain gene expression profiles were influenced by parental experience. We found little evidence to support the hypothesis that offspring prioritize their same-sex parent's experience. Parental effects varied with both the sex of the parent and the offspring in complicated and non-additive ways. Failing to account for these sex-specific patterns (e.g. by pooling sons and daughters) would have underestimated the magnitude of parental effects. Altogether, these results draw attention to the potential for sex to influence patterns of intergenerational plasticity and raise new questions about the interface between intergenerational plasticity and sex-specific selective pressures, sexual conflict and sexual selection.

The information provided by the absence of cues: insights from Bayesian models of within and transgenerational plasticity.

Empirical studies of phenotypic plasticity often use an experimental design in which the subjects in experimental treatments are exposed to cues, while the subjects in control treatments are maintained in the absence of those cues. However, researchers have virtually ignored the question of what, if any, information might be provided to subjects by the absence of the cues in control treatments. We apply basic principles of information-updating to several experimental protocols used to study phenotypic plasticity in response to cues from predators to show why the reliability of the information provided by the absence of those cues in a control treatment might vary as a function of the subjects' experiences in the experimental treatment. We then analyze Bayesian models designed to mimic fully factorial experimental studies of trans and within-generational plasticity, in which parents, offspring, both or neither are exposed to cues from predators, and the information-states of the offspring in the different groups are compared at the end of the experiment. The models predict that the pattern of differences in offspring information-state across the four treatment groups will vary among experiments, depending on the reliability of the information provided by the control treatment, and the parent's initial estimate of the value of the state (the parental Prior). We suggest that variation among experiments in the reliability of the information provided by the absence of particular cues in the control treatment may be a general phenomenon, and that Bayesian approaches can be useful in interpreting the results of such experiments.

Predictors of individual variation in reversal learning performance in three-spined sticklebacks.

Behavioral flexibility is a type of phenotypic plasticity that can influence how animals cope with environmental change and is often measured with a reversal learning paradigm. The goal of this study was to understand why individuals differ in behavioral flexibility, and whether individual differences in behavioral flexibility fit the predictions of coping styles theory. We tested whether individual variation in flexibility correlates with response to novelty (response to a novel object), boldness (emergence into a novel environment), and behavioral persistence (response to a barrier), and tested for trade-offs between how quickly individuals learn an initial discrimination and flexibility. We compare results when reversal learning performance is measured during an early step of reversal learning (e.g. the number of errors during the first reversal session) to when reversal learning performance is measured by time to criterion. Individuals that made fewer mistakes during an early step of reversal learning spent more time away from the novel object, were less bold, less persistent, and performed worse during initial discrimination learning. In contrast, time to criterion was not correlated with any of the behaviors measured. This result highlights the utility of dissecting the steps of reversal learning to better understand variation in behavioral flexibility. Altogether, this study suggests that individuals differ in flexibility because flexibility is a key ingredient to their overall integrated strategy for coping with environmental challenges.

Personality traits change after an opportunity to mate.

There is growing evidence that personality traits can change throughout the life course in humans and nonhuman animals. However, the proximate and ultimate causes of personality trait change are largely unknown, especially in adults. In a controlled, longitudinal experiment, we tested whether a key life event for adults--mating--can cause personality traits to change in female threespine sticklebacks. We confirmed that there are consistent individual differences in activity, sociability and risk-taking, and then compared these personality traits among three groups of females: (i) control females; (ii) females that had physically mated, and (iii) females that had socially experienced courtship but did not mate. Both the physical experience of mating and the social experience of courtship caused females to become less willing to take risks and less social. To understand the proximate mechanisms underlying these changes, we measured levels of excreted steroids. Both the physical experience of mating and the social experience of courtship caused levels of dihydroxyprogesterone (17α,20ß-P) to increase, and females with higher 17α,20ß-P were less willing to take risks and less social. These results provide experimental evidence that personality traits and their underlying neuroendocrine correlates are influenced by formative social and life-history experiences well into adulthood.

Effects of predation risk on egg steroid profiles across multiple populations of threespine stickleback.

Predation often has consistent effects on prey behavior and morphology, but whether the physiological mechanisms underlying these effects show similarly consistent patterns across different populations remains an open question. In vertebrates, predation risk activates the hypothalamic-pituitary-adrenal (HPA) axis, and there is growing evidence that activation of the maternal HPA axis can have intergenerational consequences via, for example, maternally-derived steroids in eggs. Here, we investigated how predation risk affects a suite of maternally-derived steroids in threespine stickleback eggs across nine Alaskan lakes that vary in whether predatory trout are absent, native, or have been stocked within the last 25 years. Using liquid chromatography coupled with mass spectroscopy (LC-MS/MS), we detected 20 steroids within unfertilized eggs. Factor analysis suggests that steroids covary within and across steroid classes (i.e. glucocorticoids, progestogens, sex steroids), emphasizing the modularity and interconnectedness of the endocrine response. Surprisingly, egg steroid profiles were not significantly associated with predator regime, although they were more variable when predators were absent compared to when predators were present, with either native or stocked trout. Despite being the most abundant steroid, cortisol was not consistently associated with predation regime. Thus, while predators can affect steroids in adults, including mothers, the link between maternal stress and embryonic development is more complex than a simple one-to-one relationship between the population-level predation risk experienced by mothers and the steroids mothers transfer to their eggs.

Individual variation and the challenge hypothesis.

In this paper I discuss how the challenge hypothesis (Wingfield et al., 1990) influenced the development of ideas about animal personality, and describe particularly promising areas for future study at the intersection of these two topics. I argue that the challenge hypothesis influenced the study of animal personality in at least three specific ways. First, the challenge hypothesis drew attention to the ways in which the environment experienced by an organism - including the social environment - can influence biological processes internal to the organism, e.g. changes to physiology, gene expression, neuroendocrine state and epigenetic modifications. That is, the challenge hypothesis illustrated the bidirectional, dynamic relationship between hormones and (social) environments, thereby helping us to understand how behavioral variation among individuals can emerge over time. Because the paper was inspired by data collected on free living animals in natural populations, it drew behavioral ecologists' attention to this phenomenon. Second, the challenge hypothesis highlighted what became a paradigmatic example of a hormonal mechanism for a behavioral spillover, i.e. testosterone's pleiotropic effects on both territorial aggression and parental care causes aggression to "spillover" to influence parenting behavior, thereby limiting behavioral plasticity. Third, the challenge hypothesis contributed to what is now a cottage industry examining individual differences in hormone titres and their relationship with behavioral variation. I argue that one particularly promising future research direction in this area is to consider the active role of behavior and behavioral types in eliciting social interactions, including territorial challenges.